The present invention relates to the formation of optical waveguides, and more particularly to improved apparatus for coating such waveguides.
As is now well known, optical waveguides comprise thin strands of an optical material such as glass, which exhibit a radially-varying index of refraction. The change in refractive index, commonly formed by the interface of two or more concentrically disposed layers of material, effects an internal reflection of light rays so that a beam of light is continually reflected or guided within the optical waveguide with a minimum of energy loss.
In the manufacture of optical waveguides, it has been found necessary to provide the guides with an appropriate coating. The coating, usually of a material having a lower refractive index than the waveguide material, serves to provide optical insulation to the waveguide and protects it from abrasion, nicks and other physical damage. In many applications a lacquer or similar coating material is used, and applied to the waveguide surface by pulling the waveguide through an applicator.
Inasmuch as waveguides are commonly formed by drawing from a glass blank and subsequently winding them upon a takeup drum or reel, it is advantageous to be able to apply the coating to the optical waveguide subsequent to drawing but before it is wound upon the reel. Otherwise, the waveguide would have to be unwound from the reel, passed through a coating apparatus, then wound upon a second reel. Due to the great length of the waveguide and its relatively fragile nature, such unnecessary handling is to be avoided if possible.
Accordingly, apparatus have been devised for applying a liquid coating to a moving strand of optical waveguide immediately after drawing, and for drying the coating before the waveguide is wound upon the takeup reel. A small die or the like having a suitably-sized aperture is commonly provided, and an enclosure provided adjacent the die for receiving liquid coating material. As an optical waveguide traverses the apparatus, it passes through a volume of the coating material. The amount of coating left on the surface of the guide is determined by the size of the die, and after emergence from the die the coated waveguide is passed through a drying station to cause the coating to solidify before the guide is wound upon a takeup reel or the like.
While the foregoing system works well in practice insofar as applying the coating is concerned, substantial difficulties arise when it is necessary to start a new waveguide through the system, or to clean accumulated chips or other foreign matter from the area of the die.
When commencing to draw a waveguide fiber from the fused end of a glass blank, it is highly desirable that the draw speed be maintained. However, in currently used systems it is necessary to cease drawing the fiber long enough to insert the leading end of the guide through the coating apparatus, and thread the guide through the necessary apertures. This procedure calls for considerable manual dexterity and practiced skill; and even with the most adept of operators the delay in drawing the strand from the glass blank often gives rise to an enlarged, globular portion in the area of the waveguide which was adjacent the drawing blank when the drawing process was interrupted. If of sufficient size, this globular portion will jam in the orifice of the coating apparatus, breaking the waveguide and necessitating a repetition of the threading process.
In other instances foreign matter, chips and the like accumulate about the coating die orifice as the waveguide is passed through the coating apparatus. Ultimately, this buildup must be removed before drawing can continue. In order to clean the orifice it is necessary to break the waveguide and pull the free end through the coating apparatus, then remove the clogged die and clean it. Upon reassembly of the coating apparatus the previously-broken leading end of the waveguide must be re-threaded through the device. This not only absorbs valuable manufacturing time, but hinders the production of extremely long waveguides. For all of these reasons, it should be apparent that it would be of great value to provide a coating apparatus for optical waveguides which does not require that a free end of a waveguide be threaded through the apparatus.
It is therefore an object of the present invention to provide an improved coating apparatus for optical waveguides.
Another object of the invention is to provide a coating apparatus for applying a liquid coating to the surface of a moving optical waveguide strand, which does not require that the strand be threaded endwise through the apparatus.
Yet another object of the invention is to furnish a coating apparatus including a generally circular aperture for receiving a moving strand, which initially receives the strand through one side thereof.
Yet another object is to provide a coating apparatus which is capable of receiving an uninterrupted length of waveguide.